Method and apparatus for attaching power line communications to customer premises

ABSTRACT

A method and apparatus for modifying a three-phase power distribution network in a building in order to provide data communication by using a Power Line Carrier (PLC) signal to an approximate electrical central location point of Wye-connected and Delta connected power distribution system remote from the data entry point of the building. A passive coupler device is attached to a centrally located service panel. The passive coupler receives the Power Line Carrier (PLC) signal from the remote entry point in the building and conditions the signal for entry at the service panel onto each phase of the three phase power distribution network.

BACKGROUND AND SUMMARY OF THE INVENTION

This application is a continuation-in-part of application Ser. No.10/219,811, filed Aug. 16, 2002 now U.S. Pat. No. 6,975,212, thedisclosure of which is expressly incorporated by reference herein.

The ability to interconnect computers and other intelligent devices is acommon requirement wherever people live and work today. The electricalconnection required to form this local area network (LAN) hastraditionally been accomplished by installing dedicated data wiring bothinside buildings and between clusters of buildings. A number of wireless(i.e. radio) methods have also been developed and deployed to addressthis need.

More recently, technology to allow electric power wiring infrastructureto simultaneously transport data at high rates has been realized. ThisPower Line Carrier (PLC) technology typically uses modulated radiofrequency (RF) signals below 50 MHz conducted on the power wiring totransport the data.

There are significant practical advantages offered by PLCtechnology—namely that electrical wiring, of necessity, must beinstalled and that data connectivity can therefore be immediately addedat little (or no) additional cost, particularly in existing buildings.Similarly, electrical outlets are ubiquitous within modem buildings andsignificant operating convenience is realized when data issimultaneously available at every outlet.

Another advantage of PLC technology is that the range that can beachieved is significantly greater than wireless methods, particularly incommercial buildings constructed of heavier materials that severelyattenuate wireless signals. Yet another advantage of PLC technology overwireless methods is that the data is inherently more secure since aphysical connection is required to join the network.

The invention described here addresses several important problems thatarise in the installation and use of PLC technology for local area datanetworks.

Most contemporary LANs are configured in a “hub and spoke” topologywhere a central server device supports a number of users and alsoprovides a gateway to the Wide Area Network (WAN) and/or the Internet.Maximum utility for a PLC network is obtained when its' physicalconfiguration mirrors the logical topology of the LAN, i.e. when the PLCgateway is effectively located at the “electrical center” of the spacesuch that every outlet is served with the best possible PLC signal. Thispoint is often a rarely accessed electrical panel in a service closet orthe basement and is almost never co-located with other data processingequipment. The invention provides a simple means to remotely inject thePLC signals at this optimal point.

Another important issue, particularly in commercial buildings, is that3-phase electrical power/wiring is commonly used and adequate coverageof a PLC network within the building is achieved only when all threephases are excited with the PLC signal. The invention provides for thesimultaneous excitation of all 3 phases of power wiring with a singlePLC signal.

Yet another related issue arises during the installation of PLC networksin environments that have natural barriers to the signals (or block thementirely). A common situation is where a building has been modified andall sections no longer share a common source of electrical power.Another common situation is where power is supplied from a central pointand then distributed to sections of the space via transformers, oftenfor purposes of distribution efficiency or electrical isolation. Theinvention also provides a simple and flexible means to inject a singlePLC signal into any number of remote points as required to obtainadequate coverage.

The system according to the present invention interfaces a communicatingsignal with a three-phase power network of a building by feeding a powerline carrier signal to a remotely located coupling device which isconstructed to enable each of the three phases to be supplied with thePLC signal from the remote signal source. In another aspect of thepresent invention, the signal can be fed to two or more different partsof a building having different electrical isolation qualities withrespect to a PLC signal by providing a separate coupling device for eachpart of the building.

Other objects, advantages and novel features of the present inventionwill become apparent from the following detailed description of theinvention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram illustrating how electrical poweris supplied to and distributed within buildings.

FIG. 2 expands a portion of FIG. 1 and illustrates how and where thecoupler constructed in accordance with the present invention ispositioned connected.

FIG. 3 is a schematic of the coupler according to the present invention.

FIG. 4 details an arrangement for improving PLC signal coverage and isan embodiment of the invention for buildings having portions which areisolated with respect to communication data.

FIG. 5 is a schematic of a coupler configuration for use in a 3-phaseWye-connected power network

FIG. 6 is a schematic of a coupler configuration for use in a 3-phaseDelta-connected power network

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the current invention are directed to improving dataconnectivity afforded by PLC technology. While the carrier currentcoupler apparatus described here provides the means to effect thephysical connection to the building power wiring, much of theimprovement derives from identifying the appropriate point(s) at whichto inject the PLC signal.

One common objective is to inject the PLC signal from a single,centralized device (often called a “gateway”) into the building wiringin such a way that all receptacles in the building receive adequatesignal for a second device (often called a “terminal”) plugged in thereto function properly. The attenuation of PLC signals along arbitraryruns of wiring is difficult to predict and highly variable so it isgenerally not possible to supply all receptacles with equal signallevels. A more achievable objective is to have the building and all ofits' receptacles taken together as a system be well-behaved, i.e. whereno single receptacle is completely cut off from the PLC signal and wherethe signal amplitude decreases in a reasonably predictable fashion withdistance from the signal injection point.

FIG. 1 shows a simplified block diagram of a building power distributionsystem and will be used to illustrate the above discussion. Electricityfrom the utility mains enters the facility via step down transformer(31) through terminal box (32) and is measured for billing purposes bymeter (33). It is then conducted to service panel (30) where it is splitand further directed to many receptacles (35) via panel boards (34). Itis certainly possible to inject the gateway PLC signal at any of theabove numbered points however the optimal point is probably servicepanel (30) because it symmetrically feeds all of the receptacles (35).PLC signal attenuated along the wiring from transformer (31) (ifinjected there) to the service panel (30) is entirely wasted since noterminal devices will ever be connected there. Similarly, injecting thegateway signal at one of the receptacles (35) could be workable but isprobably not optimal since the receptacles are probably notsymmetrically distributed about any given one.

An optimized system which maximizes use of the passive couplerarrangement is to connect the carrier current coupler (20) to servicepanel (30), inject the PLC signal from gateway (40) into the building atthat point and measure the data throughput performance at a number ofreceptacles by any commonly available means. FIG. 2 illustrates thedetails of making that connection.

Referring to FIG. 2, service panel (30) is the same as discussedpreviously. Accepted electrical safety requirements prescribed in theNational Electrical Code require that a cut-off switch (22) andfuse/circuit breaker (21) be installed. Even though only minute PLCsignal currents are expected to flow along this path, the cut-off switch(22) is necessary to protect service personnel from the power linevoltage during installation/maintenance and the fuse/circuit breakerprotects the building in event of a catastrophic failure of the carriercurrent coupler (20). Terminal block (23) provides a convenientattachment point for the wiring.

An additional dimension to be considered is the common use of 3-phasepower in commercial buildings. In this case, service panel (30) contains3 hot wires (often referred to as “L1”, “L2” and “L3”), a neutral and aground wire. The object of the original building wiring plan was tobalance the load across all 3 phases so roughly ⅓ of the receptacles(35) downstream will ultimately be connected to each of L1, L2 and L3.Therefore, to provide PLC signals to all receptacles, the signal must besplit and fed to all 3 phases simultaneously. FIG. 3 illustrates suchconnection.

FIG. 3 shows the internal details of the carrier current coupler (20).The single-ended PLC signal from the gateway is conducted via coaxialcable (17) and subsequently coupled to each power phase via baluntransformer (14) and capacitor (12). Capacitor (13) is optional and mayor may not be used. Metal oxide varistor [MOV] (11) is used to suppresspower line transients that might cause damage to the electronics in thegateway (40). Additional protection to the gateway electronics isprovided by transient voltage suppressor (16). A second fuse (15)(generally rated at very low amperage) is used to further protectagainst short circuit failure of MOV (11). The circuit includingcapacitor (12), fuse (15) and MOV (11) is simply replicated to feed all3 phases.

FIG. 5 illustrates a detailed circuit configurations when the powernetwork is a Wye-connected 3-phase power network. In a Wye-connected3-phase network, each single-phase receptacle (35) is connected to theNeutral and one of the 3 phases (A, B, or C). In the circuit 20′ of FIG.5, the 3 phases are essentially connected together in the frequencyrange of the communications signal by capacitors (12). Therefore, byconnecting the communications signal across the Neutral and thecombination node (52), the signal is from balun transformer 14′ coupledacross the two terminals of each receptacle (35).

FIG. 6 illustrates a detailed circuit configuration when the powernetwork is a Delta-connected 3-phase network. The circuit 20′ addressesthe modification required to avoid having 2 terminals of each receptacle(35) being connected together in the frequency range of thecommunication signal which would prevent signal coupling.

In order to couple the communications signal to all receptacles (35) ina Delta network, it is necessary to provide a signal voltagedifferential across all combinations of phases: A and B, B and C, & Cand A. This can be accomplished with the circuit 20″ of FIG. 6. Anunavoidable consequence of this circuit is the fact that the turns ratiofrom the Gateway (40) to one of the phase combinations (in this caseA-C) is one half the turns ratio from the Gateway (40) to the other twophase combinations (in this case A-B and B-C). To help remedy thesituation, the number of turns in the phase windings (61, 62) of baluntransformer 20″ can be adjusted in relation to the number of turns inthe Gateway (40) winding (63), such that the signal couplingeffectiveness between the Gateway (40) and all 3 two-phase combinationsis as near to equal as is practical.

If installation is completed as discussed previously and acceptable datathroughput results are obtained, no further work is necessary. On theother hand, one may find (referring once again to FIG. 1) that somereceptacles (35) will not have adequate PLC signal. Assume for thepurposes of this example that many of the receptacles (35) fed by oneparticular panel board (34) do not deliver adequate data throughputperformance. It may be possible by observation and/or analytical meansto determine why such is the case and remedy the situation. However,details of existing wiring behind walls and/or the history of priormodifications made to a building may not be readily apparent. FIG. 4(“Multi-point PLC Signal Injection”) illustrates a solution to thisproblem according to another embodiment afforded by the presentinvention.

FIG. 4 shows a PLC signal simultaneously injected at some point inaddition to service panel (30) to remedy a coverage issue. Coaxialsplitter (50) is a commonly available and inexpensive device used incable TV systems to split a broadband signal for use at two or morelocations. These devices may likewise be used to split a PLC signal. Inthis example, the PLC signal output of gateway (40) along coaxial cable(17) is split and directed via individual coaxial cables (18) and (19)to two carrier current couplers (20), one installed at service panel(30) as before and another at the particular panel board (34) havingreceptacles (35) with inadequate performance. In so doing, whateverphysical issues prevented the original PLC signal from reaching thisparticular panel board are circumvented. Further, since all of the PLCsignal power still remains inside the building, the only loss is theminimal attenuation which occurs in the coaxial splitter (50) itself.The effect of this process is therefore to provide adequate signalcoverage where before there was none and to slightly reduce the signalamplitude in the rest of the space. Any number of variations of thistechnique can then be employed to address specific PLC signal coverageissues as they are subsequently discovered.

The foregoing disclosure has been set forth merely to illustrate theinvention and is not intended to be limiting. Since modifications of thedisclosed embodiments incorporating the spirit and substance of theinvention may occur to persons skilled in the art, the invention shouldbe construed to include everything within the scope of the appendedclaims and equivalents thereof.

1. A system for interfacing a communication signal with a three phaseelectrical power network having at least one service panel, said systemcomprising: a carrier current device located at a first position andproviding a power line carrier signal; and a passive coupling deviceadapted to be connected to one of said at least one service panel forcoupling said power line carrier signal to each phase of a three phasepower distribution network, wherein said three phase power distributionnetwork is a Delta-connected three phase power distribution network; andwherein said passive coupling device includes a transformer deviceproviding a signal voltage differential across all pairs of combinationsof said three phases wherein a number of turns into output phase windingof said transformer are adjusted as a function of a number of turns inthe primary winding of said transformer in order to substantiallyequalize signal coupling effectiveness between said primary winding andeach of said pairs.
 2. The system according to claim 1, wherein said oneservice panel is a service panel which is the most electricallycentrally located service panel located in a building.
 3. The systemaccording to claim 1, wherein said passive coupling device is adapted tobe coupled to a high voltage distribution system having a voltage of atleast 277 volts.
 4. The system according to claim 1, wherein the threephase electrical power network is located in a building.
 5. The systemaccording to claim 1, wherein the service panel is remote from the firstposition.
 6. The system according to claim 5, wherein the three phaseelectrical power network is located in a building.
 7. The systemaccording to claim 5, wherein said power distribution network includesat least two service locations wherein said service location directlyconnected to said passive coupling device is the most centrally locatedof said at least two service locations with respect to the length ofelectrically wiring in said distribution network.